It is known to provide a hybrid electric vehicle (HEV) having an engine and an electric machine each operable to drive the vehicle. A controller is operable to control the vehicle to operate in one of several HEV modes or HEV powertrain modes that include an electric vehicle (EV) mode and a plurality of parallel modes.
In EV mode the engine is switched off and the electric machine is operated as a motor to apply a positive torque to a driveline of the vehicle. In a parallel boost mode the engine and electric machine both apply positive torque to the driveline. In some HEVs, in a parallel recharge mode the engine applies a positive torque to the driveline whilst the electric machine (which may for example be a crankshaft integrated starter generator (CIMG) is operated as a generator and applies a negative torque to the driveline. The engine therefore provides torque to drive the generator in addition to providing torque to propel the vehicle.
In some HEVs, a controller is arranged to control the vehicle initially to operate in electric vehicle (EV) mode until a state of charge (SoC) of the battery has fallen to a value of 50% of the battery's total capacity. The vehicle is then operated in such a manner as to sustain this SoC by assuming one of the HEV modes selected according to a particular hybrid powertrain control methodology.
A number of different hybrid powertrain control methodologies have been employed in an attempt to optimise powertrain operation. For example a methodology may seek to minimise an amount of fuel consumed by the vehicle over a given drivecycle and/or an amount of carbon dioxide emitted over the drivecycle.
It is an aim of embodiments of the present invention to improve an efficiency and drivability of a hybrid electric vehicle.